Diffusion Weighted Imaging of the Hepatobiliary System by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9783319629773
Publisher: Springer International Publishing

Regarding the perfusion-related parameters, few IVIM studies showed a relationship between f or D* and steatosis [79, 96, 124]. A decrease in f has been observed in a NAFLD/NASH rabbit model, with strong correlation (−0.83) and excellent diagnostic performance (AUC above 0.9 for any grade) [96]. In contrast, in two studies involving diabetic patients and patients with diffuse liver disease, f was found to increase when steatosis increased, with poor to moderate correlation [79, 124]. Only one study reports an effect, namely a decrease, of steatosis on D* [79]. The fact that the two studies performed in patients reported an increase in f whereas the hepatic perfusion is known to decrease in the presence of steatosis [157] may be explained by several factors. First, a dependence of f on TE has been reported, because of the T2 difference between blood and tissue [45, 79]. Second, differences in NASH between animal models and humans as well as differences in the percentage of NASH patients between studies might also partially explain the discordant results [137, 156].

In contrast, no difference in f or D* between steatotic and non-steatotic livers was observed in other IVIM studies [41, 104, 108, 137, 140, 141, 151]. Technical factors, including insufficient sampling of the low b values [108, 141, 151] and high variability of the perfusion-related parameters [104] may partially explain these observations.

From the literature, the diagnostic performance of DWI to assess steatosis is moderate at best in patients, and relies on a robust determination of D and, to a lesser extent, of f. More efficient MR methods exist to grade liver steatosis, as for example MR spectroscopy [88]. However, it only provides information from a small volume and necessitates complex post-processing [7]. Chemical-shift-based fat imaging methods with T2* correction and fat spectrum modelling has become the reference method for assessing fat content within the liver [162, 163], because of its ease of implementation and interpretation, as well as its good agreement with MR spectroscopy and histology [164–167].

While it provides information on the pathological changes occurring in tissue microstructure and microcirculation of liver steatosis, DWI with IVIM approach is not really recommended for the diagnosis and staging of steatosis. However, because of the potential effects of steatosis on ADC and IVIM parameters, steatosis has to be considered as a serious confounding factor in liver DWI studies, especially for the assessment of fibrosis, as we have shown in a recent study performed in patients with chronic liver disease that steatosis was more strongly associated with diffusion parameters than fibrosis did [41].

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